Magnetic compass



April 25, 1939.

MAGNETIC COMPASS Filed lApril 6, 1936 E. HULL 2,155,712

Mfg

ment.

Patented Apr. 25, 1939 UNITED s'l'ATr-:js

PATENT orifice- MAGNETIG COMPASS Walter E.' Huil, Warren, Ohio Application April s, 193s, serial No; 72,895

' 13 claims.

My invention relates to magnetic compasses for determining the direction of travel of auto-'- mobiles, boats, aircraft and the like.l It relates more particularly to compensating devices for` correcting semicircular deviation.

An object of my invention is to provide a compensating magnetic field, the strength of which may be varied'by rotating a magnetic element in a substantially vertical plane and shielding the vertical component oi' the rotatable field to prevent tilting of the compass card, in positions the card than the other.

where one pole is nearer Other objects arev to provide a compass with universal mounting means, attractive design an'd simple construction to facilitate economy in manufacturing.

Referring to the drawing, Figures 1 to 5, inclusive, show a preferred form of my invention. using two compensating unita which act at right angles to each other.

Figure 1 shows a front view of the compass.

Figure 2 is a cross-section taken on theline 2-2 of Figure 1, showing the compass mounted on a vertical panel. R

Figure 3 shows a section taken on the line 3 3 of Figure 2.

Figure 4 is a partial side view showing a vacuum cup mounting on a sloping glass surface such as an automobile windshield.

Figure 5 is a section taken on" the line 5-5 of Figure 1.

Figure 6 shows another `form of 'my invention using a single compensating unit which may be rotated about a vertical axis.

Figures 7, 8 and 9 are diagrams illustratingr the principle of the compensating unit. v

It is well known that magnetic compasses y mounted in automobiles, boats, aircraft and the like are aiected by local magnetism from steel and electrical equipment. To make a compass operate correctly under these conditions, it is necessary to compensate the horizontal com-l ponent of this local magnetic iield with an opposing parallel eld of the same strength. It is obvious that means must be provided for varying both the direction and thestrength of this compensating field.

ln my present invention, a magnetic element is mounted above or lbelow the compass dial, or both. The'compensating field is the horizontal component of the eld from the magnetic ele- The strength of the horizontal component is varied by rotating the magnetic element in a vertical plane. Obviously, in positions 55 `where one pole of the magnetic element is nearer (ci. azi-225) v `the compass card than the other, Athere is a vertical component which has a tendency to tilt the compass card. To reduce this vertical comporent to a negligible force, I use shields of soft iron or other highly permeablemetal.

The magnetic action of the compensating magnet and the shieldsmay bebetetr understood by referring to the drawing.

Figure 7 shows .the neutral position. The permanent magnet I is in a vertical position. Most of the magnetic ux ows from one -pole through the highly permeable shields 2 to the..other pole. VAny slight leakage will be vertical and will not noticeably aiect the compass card.

lFigure 8 shows the magnet I slightly rotated to the right. Due to the position of the gaps between theshieIds 2, part ofy the magnetic flux will flow outside of the shields producing a slight external field as shown. A

Figure 9 shows the position where the maxii mum external iield occurs.

If the magnet I is rotated to the left from the position shown in Figure 7, an external eld will be produced, flowing in theopp'osite 'direction from that shown in Figures 8 and 9.

Figure 6 vshows one practical embodiment of my invention. A compass card 3 is pivotally supported within a .casing 4. A single compensating unit is used consisting of a permanent magnet 5, semicircular shields 6 of highly. permeable metal, a housing I which srotatable about a vertical axis, and a'clamp'ing ring 8. f

To compensate the compass, the housing 1 is rotated about its vertical axis until thehorizontal component of the eld from the magnet 5 is parallel to 'the horizontal component of the ,local magnetic eld. The magnet 5 is then rotated in a vertical plane until the strength of the compensating eld in the vicinity of the compass card is equal and opposite to the strength of the local magnetic field.

Figures 1 to 5 inclusive show a preferred form of my invention. Permanent magnets 9 are secured within a compass card I0. A casing adapted to be lled with a liquid comprises a transparent. dome shaped part or cup member III with its open end threaded and a screw capl I2 which is of amr suitable non-magnetic metal. A

diaphragm I3 aliowsfor expansion and con- I traction of the liquid due to variation in temperature. The wire I4 serves as a. combined lubber line and a means for pivotally supporting the compass card I0 within the casing. This compassunit is pressed into a cylindrical cavity, in a. body or housing l5. which is of any suitable ing I5. The cap 2|Il is held in place by a U- The Washer 2l fits The shaped spring washer 2l. into the annular groove in the shaft I8.

spring washer 2| also provides a frictional means for holding the compensating unit in adjustment. The shaft I8 is held in place endwise by a screw 22. The end of the shaft is nearest the ennuier groove is provided with a. slot to facilitate turning the shaft for the purpose of adjustment.l

The lower part of the housing I5 is provided with a cavity to accommodate a. second compensating unit which operates at right'angles to the upper compensating unit. Its construction is similar to that of the upper compensating unit, except that fewer permanent magnets are necessary due to its position being nearer the compass card magnets 9. In order to make the increase in the strength of the compensating held more even as the' shaft I8' is rotated from the neutral position. the magnets I'I4 are spiraliy mounted in the shaft. Obviously, the poles of the magnets I1 do not all pass the gaps between the shields I9 on a smooth surface such as a straight or sloping atthe same position of the-shaft. 'I'his makes the adjustment near the neutral position less sensitive. To provide a balanced magnetic condition, half of the magnets are spiraled to the right and half to the left. The neutral position occurs where the resultant of the fields from the magnets I1 is vertical. The maximum compensating ileld occurs when the resultant eld is horizontal.'

To explain the operation of the compensating units, I shall consider the compass as being mounted in an automobile. The horizontal component of the local magnetic field may be considered as comprising a lateral component and a longitudinal component. 'I'he longitudinal component is neutralized by the iield from the upper compensating unit. 'Ihe lateral component is neutralized by the field from the lower compensating unit. The adjustment may be accomplished by first heading the automobile north and rotating the shaft 23 to the position where shaft la. v

Another feature of the compass shown is a novel universal bracket for mounting the com'- pass. It permits mounting the' compass on an oblique angled siu'face such as a header board of an automobile, by means of screws. `It also provides a detachable vacuum cup for mounting V windshield. 'I'he bracket 24 comprises a disc and a ball connected by a tapered shank. It may be of any suitable metal such as brass. The

disc is provided with holes to accommodate screws 25 and a tapped hole to accommodate the screw insert 2Q in the rubber vacuum cup 21. -Th

anemia housing Ii is provided with a cavity suitable to accommodate theball onthe bracket 24. Aset screw 28 is provided with a cupped end which ifrlctionally engages the ball on-the bracket 24',

net about a transverse axis thereof and in a substantially 'vertical plane and -shlelding means comprising spaced shield sections disposed rela'- tive to said compensating magnet to reduce the vertical force component of the external eld compensating magnet, said shield sections being disposed to surround the compensating magnet with their adjacent edges spaced apart to define slots lying in a vertical plane extending through said transverse axis. l V

2.A compass unit comprising a transparent.

dome-shaped, threaded casing, a threaded cap for said' casing and forming therewith a compass unit, and acompass card within said casing, 'a housing having substantially cylindrical cavities adapted to receive respectively said compass unit and a compensating means, compensating means within one cavity of said housing, and ribs within said other cylindrical cavity to fricti'onally engage said threaded cap.

3. In a magnetic compass, a body having a recess therein, and a compass unit disposed in said recess comprising'a transparent cup member having a cap. applied thereto 'to close the open end and a card pivotally supported'in said, cup member, said body having spaced projections extending axially of the recess on the inner wall thereof and engaged by said cap for retaining said unit in the recess. s

4. In a magnetic compass, e body having e. cavity extending thereinto from the front thereof and an elongated cavity therein with its axis lying substantially horizontal and vertically oif' set from the axis of the first mentioned cavity, a'

compass unit in the rst cavity comprising a casing having a transparent wall and apivoted card therein, a. highly permeable substantiels cylindrical shield disposed in and forming a lining for said elongated cavity, said shield comprising sections disposed with edges thereof spaced apart to form vertically spaced slots, and

a compensating magnet Within said elongated cavity and surrounded by said shield.

5. In a magnetic compass, a body having a.`-

cavity extending thereinto from the front thereof and a laterally elongated cavity therein above the iirst mentioned cavity, a compass unit in the rst cavity comprising a transparent wall and a pivoted card inwardly thereof, a highly 'permeable shield in the second cavity comprising correspondingly elongated, opposed shield sections disposed with portions thereof spaced to form a slot-like opening 4in the shield at the side thereof nearesty the compass unit, a rotatable shaft disposed substantially coaxially of said second cavity, and a plurality of permanent magnets carried by said shaft and extending transversely of said second cavity between said shield sections.

6. In a magnetic compass. a body having a main cavity extending thereinto from the front thereof and also having elongated cavities therein above and below the Vmain cavity and disposed with their axes extending substantially horizontal and at right angles to each other, a, compass unit in said main cavity comprising a transparent wall and 4a pivoted card inwardly thereof, a highly permeable shield in each elongated cavity comprising opposed shield sections disposed with adjacent edges thereof spaced to form a slot-like opening in the shield at the side thereof neart vthe compass unit, and a permanent magnet in each elongated cavity between the shield sections thereof and supported for rotative adjustment about its transverse axis.

7. In a magnetic compass, a body having a mainl cavity extending thereinto from the front thereof and also having elongated cavities therein above and below the main cavity and disposed with their axes extending substantially horizontal and at right angles to each other, a `compass unit in said main cavity comprising a transparent wall and a pivoted card inwardly thereof, a highly permeable shield in each elongated cavity comprising substantially semicylindrical vcomplemental shield elements having their adjacent edges spaced apart to form vertically spaced horizontally extending slots, a rotatable shaft supported in each elongated cavity substantially coaxially of the shield thereof, and a plurality of permanent magnets carried by each shaft and extending transversely of the shaft.

8. In a magnetic compass a body having subvstantially cylindrical cavities extending thereinto, a compass unit in one cavity comprising a transparent cup member and a pivoted card therein, complemental substantially semicylindrical shield elements disposed in said other cavity with their edges spaced -apart to'form vertically spaced horizontally extending slots, a rotatable shaft supported substantially coaxially of said other cavity, and a permanent magnet carried by said shaft and extending transversely of said other cavity between the shield elements thereof.

9. In a magnetic compass a body having a cavity and a pivoted card therein, said body also having an elongated cavity therein with its axis lying in a substantiallyhorizontal plane which is vertically spaced from the card, and a shaft extending axially in said elongated cavity and carrying a compensating magnet. said shaft and body having cooperating portions whereby the shaft is rotatable in said cavity and adapted to be held in av desired position of adjustment including axially spaced thrust shoulders on the shaft one of which is a spring washer.

10. Iny a magnetic compass a body having a cavity and a pivoted card therein. said body also having an elongated cavity therein with its axis lying in a substantially horizontal plane which is vertically spaced from the card, a cover adapted to close one end of said elongated cavity and having an' opening for substantial alignment with an opening in'the'opposite end wall of said elongated cavity, a shaft rotatably supported in such rated to define a slotted horizontal cylinder with the slots in a vertical plane, a permanent magnet diametrically ,disposed between said shields. and means mounting said permanent 'magnet for rotation. about an axis substantially coincident with the axis ofsaid cylinder.

12. A compensating device for compasses comprising a pair of compensating units acting at .right angles to each other, each of said compensating units comprising a pair of stationary highly permeable complemental substantially semicylindrical shieldsA with their edges spaced to form. a vlongitudinally slotted'cylinder, a permanent magnet diametrically disposed between said shields, and means mounting said permanent mnet for rotation about the axis of said cylin r.

13. A compass compensating device comprising a pair of compensating units acting at right angles to each other, each compensating unit comprising a pliu'ality of magnets with their endsV Y disposed on a spiral about a common horizontal 1 axis and with the center of each magnet lying substantially on said axis, said magnets being disposed at substantially right angles to said axis, .and means providing for rotation of said magnets in substantially vertical planes about said common horizontal axis.

, WALTER E. HULL. 

